JP2003297542A - Resonance type induction heating device and fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonance type induction heating device that can realize an appropriate heating distribution corresponding to heating condition on the heating roller and is of low cost, and a fixing device that uses the heating roller of this device. <P>SOLUTION: The resonance type induction heating device having a plurality of resonance capacitors that bring about resonance with an induction heating coil comprises a heating condition judgement means for judging the heating condition of the heating object, a heating coil selection means for selecting the induction heating coil and the resonance capacitor to be flown current by the output of the heating condition judgement means, and a current supply means for flowing current to the induction heating coil and the resonance capacitor selected. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plurality of induction heating coils which are built in a heating roller and arranged in the axial direction, a plurality of resonance capacitors which resonate with the induction heating coils, and an alternating current to the induction heating coils. The present invention relates to a resonance-type induction heating device having a power switching element that supplies electric power, and a fixing device that applies the resonance-type induction heating device to fix heat-meltable powder such as toner to a sheet as a heated object.

[0002]

2. Description of the Related Art In an electrophotographic copying machine / printer or the like, toner electrostatically adsorbed on a sheet (material to be heated) as a print medium is formed on the sheet by a fixing device as shown in FIG. It is fixed by heat and pressure. In the structure of the fixing device, a heating roller 501 and a pressure roller 502 are arranged to face each other, and a sheet on which toner is electrostatically adsorbed is passed between the two rollers. At this time, the toner is heated by the heating roller 501 and pressed by the pressure roller 502 and the heating roller 501 to be fixed on the paper. A sensor TH1 for temperature detection is attached to the heating roller 501, detects the temperature of the surface of the heating roller, and controls the heating device to reach a desired temperature.

Various methods have been devised as a heating device in a heating roller used in a copying machine / printer or the like. As the heat source, there are an example using a halogen heater and an example using an induction heater.

In an electrophotographic apparatus such as a conventional copying machine / printer, it is proposed to use an induction heating method which is excellent in high-speed start-up of the fixing device (the device temperature is controlled to a desired value in a short time). Is increasing. Generally, in the induction heating device, it is necessary to switch a large amount of electric power at a high speed, so that the switching loss (power loss generated when the switch element turns on or off) becomes large, and the switch element is The temperature rises excessively and the reliability of the switch element decreases.

In order to prevent this problem, a resonance type inverter, which is a system with less switching loss, is used. In this resonance type inverter, zero cross switching is realized by utilizing the resonance phenomenon of the resonance coil (induction heating coil) and the resonance capacitor. In order to perform zero-cross switching, it is necessary to select an appropriate resonance capacitor capacity for the resonance coil.

FIG. 3 is a schematic block diagram of a general induction heating device which realizes zero-cross switching, and FIG. 4 shows voltage and current waveforms of respective parts during operation of the device. In FIG. 3, 100 is a heating roller (object to be heated) in the case of a copying machine / printer, and 200 is an induction heating power source. L1
Is an induction heating coil for inducing an induction current in the heating roller 100, and TH1 is a temperature sensor for detecting the temperature of the heating roller 100.

In the induction heating power source 200, the AC output from the AC power source 1 is connected to a rectifier circuit 2 composed of diodes D1 to D4, and a capacitor connected between a noise filter NF1 connected to the output terminal of the rectifier circuit 2. C1, a capacitor C2 connected in parallel with the induction heating coil L1, a power switching element Q1 (IGBT or the like is used) connected in series with the induction heating coil L1, and a diode D5 connected in parallel with this power switching element Q1. , A temperature detection circuit 7 for inputting the detection output of the temperature sensor TH1,
A resonance control circuit IC1 which receives the output signal of the temperature detection circuit 7 and outputs a control signal for the power switching element Q1. Further, the resonance control circuit IC1
Is composed of a triangular wave generation circuit 3 and a comparison circuit 4 for comparing the output signal of the triangular wave generation circuit 3 and the output signal of the temperature detection circuit 7.

The operation of the induction heating device having the above construction will be described below.

When the heating command signal is sent to the induction heating power source 200, the frequency 2 is output to the output terminals 5 and 5 of the induction heating power source.
High frequency AC power of about 0 KHz to 100 KHz is generated. This AC power is applied to the induction heating coil L1, and the induction heating coil L1 generates an AC magnetic field.

At this time, the AC power applied to the induction heating coil L1 varies depending on the heating roller 100, but normally 2
It is about 0 to 300 W to several kW. The AC magnetic field generated by the AC power applied to the induction heating coil L1 generates an eddy current in the heating roller 100. Joule heat is generated in the heating roller 100 by the eddy current, so that the heating roller generates heat. This electromagnetic induction action causes the heating roller to generate heat and the temperature of the heating roller rises.

Here, the temperature measurement element TH1 for measuring the temperature of the heating roller and the temperature detection circuit 7 monitor the temperature rise of the heating roller at any time, and the detected temperature of the heating roller is fed back to the resonance control circuit 1C1. The induction heating power source 1
Then, the temperature of the heating roller 100 is made constant by using a control method such as proportional control or the like, which compares the set target temperature with the detected temperature and lowers the applied high frequency power when the detected temperature approaches the set target temperature. keep.

The operation state of each part at this time will be described with reference to FIG. When the power switching element Q1 is turned on at time T1, the drain current of the power switching element Q1 increases. When the drain current reaches Io at time T2 and the power switching element Q1 is turned off at time T2, the induction heating coil L1 moves the power switching element Q1.
The current flowing in 1 is commutated to the capacitor C2 and L1,
A resonance phenomenon occurs due to C2. At this time, the drain-source voltage of the power switching element Q1 becomes a voltage waveform like a part of a sine wave due to the resonance operation of L1 and C2.

When the power switching element Q1 is turned off at time T2, the drain voltage of the power switching element Q1 slowly rises from zero volt, and no temporal overlap with the drain current occurs. Therefore, the product of the drain voltage and the drain current becomes zero, and the switch-off loss of the power switching element Q1 does not occur in principle.

After the resonance operation of the induction heating coil L1 and the capacitor C2, the resonance current is inverted at time T3 and the drain voltage starts decreasing. At time T4, the drain voltage of the power switching element Q1 becomes zero. The drain of the power switching element Q1 is clamped to zero volt by the flywheel diode D5. If the power switching element Q1 is turned on again while the current is flowing through the flywheel diode D5, that is, between times T4 and T5, the switch is turned on at the drain voltage of zero. Will be zero.

As described above, by using the resonance circuit including the induction heating coil L1 and the capacitor C2, the switching loss of the power switching element Q1 can be reduced (in principle, zero). Further, when the above-mentioned resonance switching is performed, the resonance frequency is determined by the induction heating coil L1 and the capacitor C2. Therefore, in the switching of the power switching element Q1, the Q1 off time of the power switching element becomes a substantially constant value. The control of the power input to the induction heating coil L1 is realized by controlling the on-time of the power switching element Q1.

Next, the zero-cross switching in the resonance switching will be described. In the LC resonance circuit, the power supply voltage is Vin, the drain current immediately before the power switching element Q1 is turned off is Io, and the power switching element Q is
If the drain voltage of 1 is Vo and the flywheel diode D5 is not present, it is known to operate as follows. When the flywheel diode D5 is present, it may be considered that the negative voltage portion is clamped to zero volt.

The resonance frequency ω and the resonance impedance Z in the LC resonance circuit are as follows.

Resonance impedance Z = √ (L / C) Resonance frequency ω = 1 / {√ (L * C)} The drain resonance voltage V0 is       V0 = Vin + √ (Vin ^ 2 + Io ^ 2 * Z ^ 2)             * SINω (t−θ) (1) Formula However, tan θ = Vin / (Io * Z) From the above equation, the following can be said as characteristics of resonance.

(A) The resonance voltage swings around the input voltage Vin.

(B) The resonance amplitude voltage increases as the resonance impedance Z increases if the drain current Io immediately before the power switching element Q1 is turned off is constant.

(C) If the resonance impedance Z is constant, the resonance amplitude voltage increases as the drain current Io immediately before the power switching element Q1 is turned off increases.

(D) In order to increase the power input to the induction heating coil, it is necessary to increase the drain current Io immediately before the power switching element Q1 is turned off.

Further, in the heating roller in the fixing device of the electrophotographic apparatus such as a copying machine / printer, it is necessary to realize an appropriate temperature distribution according to the heating conditions such as the paper size. For example, when fixing to a small size paper (postcard etc.) against the width of the fixing device (effective length of the heating roller),
The heat generation at the central portion of the fixing device is increased and the heat generation at the end portions is reduced. Otherwise, if the temperature of the central portion of the heating roller where the heat is absorbed by the small size paper is controlled to a desired value, the temperature of the end portion of the heating roller where the heat is not absorbed by the paper becomes excessively high.

On the other hand, in the case of fixing on a sheet of the same size as the width of the fixing device, it is necessary to make the heat generation at the center of the fixing device equal to the heat generation at the end. If the amount of heat generated at the end portion of the heating roller is smaller than that at the central portion, only the end portion of the fixing device does not reach a sufficient temperature, so that the end portion of the paper sheet fails in fixing. Thus, controlling the heat generation distribution of the fixing roller according to the paper size is indispensable for handling various sizes and types of paper.

In order to realize a desired heat generation distribution for the heating roller, as shown in FIG. 5, independent induction heating coils L1, L2, L3 are provided at the central portion and the end portion of the fixing device, and the temperature is controlled independently. A method of performing the above is considered, and desired characteristics can be obtained. In FIG. 5, TH
Reference numeral 1 is a temperature sensor that detects the temperature of the central portion of the heating roller 100, TH11 is a temperature sensor that detects the temperature of the end portion of the heating roller 100, and 17 is a measurement circuit that inputs the detection output of the temperature sensor TH1 and measures the temperature. , 171 is a measurement circuit for measuring the temperature by inputting the detection output of the temperature sensor TH11, Q1 is a power switching element connected in series with the induction heating coil L1, and Q11 is the induction heating coils L2 and L3.
Power switching elements, IC1, I, connected in series with
C11 is a resonance control circuit that outputs an ON / OFF signal to the power switching elements Q1 and Q11, and the same parts as those in FIG. 3 are denoted by the same reference numerals and duplicate description will be omitted.

[0026]

The conventional resonance type induction heating apparatus realizes zero-cross switching in order to reduce switching loss due to ON / OFF of the power switching element. However, in order to perform zero-cross switching, it is necessary to select an appropriate resonance capacitor capacitance for the resonance coil, and a plurality of power switching elements, a plurality of resonance control circuits, etc. are required, which is a cost disadvantage. There was a problem.

The present invention has been made in order to solve the above-mentioned conventional problems, and is a low-cost resonance type induction heating apparatus capable of realizing an appropriate heating distribution on a heating roller according to heating conditions. An object is to provide a fixing device using a heating roller.

[0028]

SUMMARY OF THE INVENTION The present invention is a resonance type induction heating apparatus and a fixing apparatus having the following configurations.

(1) A plurality of induction heating coils built in the heating roller and arranged in the axial direction, a plurality of resonance capacitors that resonate with the induction heating coils, and power for supplying AC power to the induction heating coils. In a resonance type induction heating device having a switching element, a heating condition judging means for judging a heating condition of an object to be heated, and a heating coil selection for selecting an induction heating coil and a resonance capacitor to be energized by an output of the heating condition judging means. In the resonance type induction heating device according to (2) or (1), a heating condition is determined by: a means and a current supplying means for energizing the selected induction heating coil and the resonance capacitor. The resonance type induction heating apparatus is characterized in that the means determines by using information on the size, type or number of heated objects.

(3) In the resonance type induction heating apparatus described in (1), the heating condition judging means determines the heat generation distribution of the heating roller. (4) The toner image formed on the object to be heated is heated and fixed to the object to be heated by applying the heating roller of the resonance type induction heating device according to any one of (1) to (3). A fixing device characterized by:

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings.

(Embodiment) FIG. 1 is a schematic block diagram of a resonance type induction heating apparatus according to a first embodiment of the present invention. In FIG. 1, L1, L2 and L3 are heating rollers 100 made of a magnetic material. L1 is an induction heating coil that induces an induction current in the center of the heating roller.
2 and L3 are arranged at the end of the heating roller 100.

C2 is a capacitor as a resonance element with the induction heating coil L1, and C3 is a capacitor as a resonance element with the induction heating coils L2, L3. SW1 is a switch that is turned on / off according to the heating condition. When the switch SW1 is off, an induction current is generated in the central portion of the heating roller by the resonance current of L1, C2, and the power switching element Q1, as described above. The Joule heat generated by the eddy current can be used to heat the central portion of the heating roller.

When the switch SW1 is on, L2,
L3 and C3 are connected in parallel with L1 and C2. Similarly, in addition to the central portion of the heating roller by the resonance current of L1, L2, L3, C2, C3 and the power switching element Q1, an induced current is also generated at the end portion of the heating roller to generate Joule heat due to the eddy current as described above. It is possible to generate heat at the center and the end of the heating roller.

The diodes D1 to D4 and the capacitor C1 are a rectifying circuit for rectifying AC power and converting it into a pulsating current, and the pulsating current is supplied to the induction heating coil L1 according to the switching of the power switching element Q1. Switch SW1
Needless to say, in the conductive state, the induction heating coils L2 and L3 are energized in addition to the above L1.

A resonance control circuit IC1 for controlling a switching state of the power switching element Q1 is connected to a control terminal thereof, and a flywheel for rectifying a flywheel current from the induction heating coil when the power switching element Q1 is turned off. The wheel diode D5 is a power conversion circuit connected in anti-parallel, and constitutes a power supply circuit for supplying heating power to the induction heating coil.

Here, since it is sufficient to switch the switch SW1 for each job such as copying / printing (every time the paper size is switched), an element having a slow switching speed (a relay is also possible) can be used. Reference numeral 7 is a measuring circuit for inputting a detection signal of the temperature measuring element TH1 to measure the temperature of the central portion of the heating roller 100, 8 is a heating condition judging circuit for receiving a heating condition input such as paper size, and 9 is a resonance condition switching circuit. is there.

Next, the operation will be described.

Based on the heating conditions (paper size, paper type, number of sheets, etc.), the heating condition judging circuit 8 judges whether the resonance condition should be the heat generation only in the central part of the heating roller or the entire heat generation including the end part of the heating roller. Then, by using the resonance condition switching circuit 9 and the switch SW1, the induction heating coils L2, L3, C
3 may or may not be connected in parallel with L1 and C2.

Then, the heating condition judging circuit 8 judges whether heat generation at the end of the heating device is necessary or whether heat generation at only the central part of the heating device is appropriate, and only the heat generation at the central part is made. When appropriate, the switch SW1 is opened so that the induction heating coils L2, L3, and C3 are not energized, so that heat generation at the end of the heating roller is stopped. Further, when heat generation at the end of the heating device is required, the switch SW1 is closed and the induction heating coils L2, L are connected.
By energizing C3 and C3, heat is generated not only at the center of the heating roller but also at the end of the heating roller. Note that the same parts as those in FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted.

When the induction heating coils L1, L2, L3 are connected in parallel, the drain current Io immediately before the power switching element Q1 is turned off increases, the resonance impedance Z decreases, and the resonance frequency increases.

More specifically, the equation (1) may be calculated. If L1 = L2 = L3, then the drain current Io immediately before the power switching element Q1 is turned off.
Is about 3 times the resonance impedance Z, and the √ (1/3) times the resonance frequency ω is √3 times, resulting in the resonance voltage p−p value √ (Vin̂2 +
Io ^ 2 * Z ^ 2) is √ (Vin ^ 2 + 9 * Io ^ 2 * 1/3 * Z ^ 2) = √
(Vin ^ 2 + 3 * Io ^ 2 * Z ^ 2) becomes larger.

As is clear from the above calculation (if L1 =
(If L2 = L3), the resonance frequency becomes about 1.7 times and the resonance voltage also increases, so that the power switching element Q1 requires a high withstand voltage and high speed element. Of course, to do zero-cross switching,
The switching frequency of the power switching element Q1 and the off time of the power switching element (as described above, L1, L
Needless to say, it is necessary to appropriately change (determined by L, C synthesized by 2, L3).

Therefore, induction heating coils L1, L2, L3
, Are connected in parallel, the resonance capacitors C2 and C3 are also connected in parallel to synthesize an appropriate resonance capacitor capacitance, so that the resonance frequency ω and the resonance voltage pp value √ (Vin ^ 2
It is desirable that + Io ^ 2 * Z ^ 2) be an appropriate value. As described above, when L1 = L2 = L3, C3
= 2 * C2 is selected, the resonance frequency ω = 1 / {√ (L * C)} = 1 / {√ (1/3 * L1 * 3 * C2)} = 1 / {√ (L1 * C2)} Resonance impedance Z = √ (L / C) = √ {1/3 * L1 / (3 * C2)} = 1/3 * √ (L / C) Resonance voltage p-p value √ (Vin ^ 2 + Io) ^ 2 * Z ^ 2) = √ (Vin ^ 2 + 9 * Io ^ 2 * 1/9 * Z ^ 2) = √ (Vin ^ 2 + * Io ^ 2 * Z ^ 2), and only L1 and C2 are connected. In this case (when only the central portion of the heating roller is heated), the same frequency and the same resonance voltage pp value are obtained, which is convenient.

As a feature of the heating device control, it is possible to determine the heat generation distribution to be realized according to the type and size of the paper selected before starting the heating operation. This means that it is possible to select the optimum induction heating coil in accordance with the heat generation distribution to be set in the future and to determine the optimum resonance capacitor condition in advance.

For example, in a copying machine, the copy start key is pressed after the user sets the number of copies and sheets. When a narrow paper such as a postcard is selected, only the induction heating coil in the central portion of the heating device may be selectively connected in advance, and the optimum resonance capacitor may be connected to the coil.

When A3 size paper or A4 landscape paper is selected, both the induction heating coil at the center of the heating device and the induction heating coil at the end are selectively connected in advance, and they are connected in parallel. It suffices to connect an optimum resonance capacitor to the coil.

In the above example, the three induction heating coils L1,
This is an example of using L2 and L3 and two resonance capacitors C2 and C3, but the case of using four or more induction heating coils to more finely control the heat generation distribution of the heating roller may be considered in the same manner.

The heating roller 100 of the resonance type induction heating apparatus according to the above embodiment is replaced with the heating roller 5 of the fixing apparatus shown in FIG.
When used as 01, it is possible to obtain a fixing device that can always perform an appropriate fixing process.

[0050]

As described above, according to the present invention,
In a resonance-type induction heating apparatus having a plurality of induction heating coils, a plurality of resonance capacitors that resonate with the induction heating coils, and a power switching element that supplies AC power to the induction heating coils, a toner to be heated on a body to be heated. Heating condition determining means for determining the fixing condition, heating coil selecting means for selecting the induction heating coil and the resonance capacitor to be energized by the output of the heating condition determining means, and the selected induction heating coil and the resonance capacitor. Since it is configured to include an energizing means for energizing, the resonance frequency and the resonance voltage p-p value can be adjusted by appropriately changing the resonance capacitor capacity at the same time when determining the induction heating coil to be energized according to the heating condition. Can be selected appropriately. As a result,
It is not necessary to increase the speed and withstand voltage of the power switching element, and the temperature sensor, the temperature measurement circuit, and the resonance control circuit for controlling the ON / OFF of the power switching element can be shared, and the cost can be reduced. Further, since the switch for selecting the induction heating coil may be an element (relay may be used) having a slow switching speed, there is an effect that it can be realized at relatively low cost and with low loss.

According to the present invention, the heating condition judging means is constituted so as to judge by using the information on the size, kind or the number of heated objects to be heated. Therefore, there is an effect that an appropriate heat treatment can be always carried out. is there.

According to the present invention, the heating condition determining means is configured to determine the heat generation distribution in the axial direction of the heating roller, so that an appropriate heat generation distribution can always be obtained in the heating roller axial direction. There is.

According to the present invention, the toner image formed on the object to be heated is heat-fixed to the object to be heated by applying the resonance type induction heating device of the present invention. There is an effect that various fixing processes can be performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a resonance type induction heating device according to a first embodiment of the present invention.

FIG. 2 is a structural diagram of a fixing device to which an induction heating method is applied.

FIG. 3 is a basic schematic configuration diagram of an induction heating device.

FIG. 4 is a voltage / current waveform diagram of each part during operation of the induction heating device of FIG.

FIG. 5 is a schematic configuration diagram of a general induction heating device that realizes conventional zero-cross switching.

[Explanation of symbols]

L1, L2, L3 Induction heating coils C2, C3 Coil resonance capacitor Q1 Power switching element SW1 Induction heating coils L1, L2, L3 energizing switch 7 Measurement circuit IC1 Resonance control circuit TH1 Temperature detection sensor

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Claims (4)

[Claims] 1. A plurality of induction heating coils built in a heating roller and arranged in the axial direction, a plurality of resonance capacitors that resonate with the induction heating coils, and power switching for supplying AC power to the induction heating coils. In a resonance type induction heating device having an element, a heating condition judging means for judging a heating condition of an object to be heated, and a heating coil selecting means for selecting an induction heating coil and a resonance capacitor to be energized by the output of the heating condition judging means. And a selected induction heating coil and energizing means for energizing the resonance capacitor. 2. The resonance type induction heating apparatus according to claim 1, wherein the heating condition judging means judges by using information on the size, type or number of heated objects. . 3. The resonance type induction heating device according to claim 1, wherein the heating condition determining means determines the heat generation distribution of the heating roller. 4. A toner image formed on an object to be heated,
A fixing device, wherein the resonant induction heating device according to any one of claims 1 to 3 is applied to heat and fix the object to be heated.